Potato tubers are harvested, allowed to suberize at warm temperatures for about 10 days, gradually cooled down to the storage temperature of about 10.degree. C. For the first 1-2 months after harvest, the tubers remain dormant and exhibit little inclination to sprout. However, after this period the tubers must be chemically treated to prevent sprouting as sprouting cause numerous deleterious effects to the tubers. These include a loss of fresh weight, the conversion of starch to sugars, and a decrease in the quality and appearance of tubers. Sprouts and the surrounding tissue also contain elevated levels of toxic glycoalkaloids, which are not destroyed by cooking. Forsythe et al. suggested that sprouting of stored potatoes may be eliminated or minimized by a treatment with chlorpropham (CIPC, 1-methylethyl-3-chlorophenylcarbamate) and DMP (dimethylnaphthalene) (U.S. Pat. No. 5,965,489, 1999). CIPC is currently used to control sprouting by the industry. Although CIPC has been used effectively for over three decades, questions concerning its toxicity have been raised, and it is currently under review by the Environmental Protection Agency. CIPC is known to be among the three pesticides found in the highest concentrations in the diet of an average American [Gartrell et al. J.Assoc. Off. Anal. Chem. 69: 146-159, 1986] and comprises over 90% of the synthetic residues found in U.S. potatoes [Klocke et al., J. Chem. Ecol. 13: 2131-2141; 1987]. Therefore, a pressing need exists to find other, more environmentally acceptable sprout inhibitors for tubers. Currently, several research groups in the United States and Europe are investigating alternative chemical inhibitors Rama and Narasimham, J Food Sci Technol., 24: 40-42, 1987; Aliaga and Feldheim Ernahrung, 9: 254-256, 1985 and ; Feldheim, "Practicability and mode of action of quality storage of potatoes after harvest" in Report of the lecture given to the German Institute for quality research [Plant Nutrition Products; March 1985, 6 pages] reported that oil from the Muna plants from south America was more effective than CIPC in inhibiting sprouting, fresh weight loss, and the incidence of rotted tuber parts over a period of 120 days. The authors also reported that the main components of the oil, including the monoterpenes alpha and beta-pinene and limonene, and the oxygenated monoterpenes pulegone and menthone/isomenthone are effective in this regard. Vaughn et al. reported a method for inhibiting sprouting of tubers including the step of exposing tubers to the oxygenated monoterpenes ("Inhibition of potato sprouting using volatile monoterpenes" U.S. Pat. No. 5,139,562, 1992.).
Some plants release certain chemicals in their immediate environment, which inhibit or stimulate nearby growing plants. The phenomenon is referred to as allelopathy and such plants are known as allelopathic plants (Bagchi et al., Phytochemistry, 45: 1131-1133 1997, koitabshi et al., J. Plant Res, 110: 1-6, 1997). A variety of allelochemicals have been identified including phenolic acids, coumerins, terpenoids, flavonoids, alkaloids, glycosides etc. (Putnam and Tang (ed.), The Science of Allilopathy, John Wiley & Sons, N.Y. 1986, Rice, Allelopathy, 2.sup.nd ed. Academic Press, New York, 1984). The chemicals are considered as resources for developing herbicides, plant growth stimulators and pharmaceuticals. The allelopathic potential of volatiles from Echinacea angustifolia have been examined on lettuce seeds. (Viles & Reese Environ. and Expt Botany, 366:39-43, 1996). Certain aldehydes such as citral, cinnamaldehyde, salicyladehyde, and benzaldehyde may be inhibitors of growth and germination (Steward & Krikorian, Plants, chemicals and growth, 1971 Academic Press, New York and London).
Salvia is known to produce volatile inhibitors. The air around Salvia has been reported to contain two terpenes i.e. cineole and camphor. Cineole inhibited germination and growth of Brassica compestris (Koitabashi et al., J. Plant Res. 110,: 1-6, 1997). The inhibitory action of volatile oil and its constituents of Thymus capitatus was tested on its own seed germination. Seed germination and seedling growth was inhibited (Vokou et al., Acta Oecol Plant, 7: 157-163, 1986). Extract of Acori rhizoma and Acorus calamus was shown to inhibit germination of lettuce seeds. (Nawamaki el al. 1996, Phytochem. 43: 1175-1182). Essential oil of H. ringens showed significant anti-germinating properties (Von Poser et al. 1996, J. Agric. & Food Chem, 44: 1829-1832). The oil of H. ringens is constituted mainly by pulegone. Reynolds reported comparative effects of acyclic compounds and quinones on inhibition of lettuce fruit germination (Ann. of Bot. 60: 215-223). Owen Asplund reported `Monoterpenes: Relationship between structure and inhibition of germination (Phytochemistry 7: 1995-1997, 1968).
The allelopathic activity of the essential oils of three Nigerian medicinal plants have been examined (Oguntimen et al 1989, Planta Medica 55: 219). Piper guineese oil showed mild root inhibition from 25 ppm to 100 ppm. Above 100 ppm, the inhibition was significantly higher i.e. 50% at 400 ppm and 57% at 800 ppm. Effect of certain essential oils and four monoterpenoids has been examined on sprouting of stored potato tubers at room temperature. The essential oils of peppermint, ajowain, basil, spearmint and monoterpenoids such as carvone, linalool, methyl chavicol and anethol were the most effective (Singh et al. 1997, Pesticide Res J 9: 121-124). An antitsprouting agent for potatoes based on the essential oil of caraway (rich in carvone) has been suggested (Capelle et al. 1997, Rev. A & M plants 3(3) no. 1452 pp 183). De Vries has reported that a combination of carvone and one or more fungicides leads to synergistic effect for inhibiting sprouting (U.S. Pat. No. 6,001,773, 1999). Benzaldehyde, salicylaldehyde and substituted benzoic acids have been found in uncooked and baked potato tubers [Coleman et al., J. Agric. Food Chem., 29: 42-49 (1981)]. These compounds have been shown to be inhibitory to the growth of plants, fungi, and bacteria. [Kurita et al. Agric. Biol. Chem. 45: 954-952, 1981].
The above described chemicals used for checking sprouting of potatoes suffer from number of disadvantages
1. Some chemicals do not show 100% inhibition of potato tubers PA1 2. The chemicals are not easily available in the market as they are not industrially produced PA1 3. Chemicals are costly. PA1 4. CIPC is synthetic chemical and its residue is left in the tubers which is harmful for human body. PA1 1. Cymbopogon martini which has high content of geraniol, geranyl acetate PA1 2. C.flexuosus with high content of citral PA1 3. C.winterianus rich in citronellal and citronellol PA1 4. Mentha arvensis with high content of menthol and menthone PA1 5. Ocimum sanctum rich in ketone, camphor PA1 6. Mentha piperita has high content of menthone and menthol PA1 7. Artemisa annua rich in ketone camphor PA1 8. Eucalyptus citradora rich in cineole PA1 9. Lavendula officinalis rich in linalool PA1 10. Cederus deodara with high content of chavicol
To overcome the drawbacks in the prior art, the applicants have developed a novel formulation useful as an anti-sprouting agent for inhibiting tuber sprouting without necrosis or softening of the tuber, especially in potatoes.